For the material for contact components or battery components, steel plates (including steel strips) such as Cr-containing steel plate, surface-treated steel plate, and the like are widely used. For use intended for contact components, contact resistance value, solderability, and the like are considered important. For use intended for battery components, corrosion resistance, workability, and the like are considered important. In general, as the steel plate intended for use for contact components, various types of surface-treated steel plates (e.g., nickel-plated steel plate, tin-plated steel plate, or copper-plated steel plate) and the like are used, from the perspective of obtaining low contact resistance value and good solderability. On the other hand, as the steel plate intended for use for battery components, Cr-containing steel plates, surface-treated steel plates (nickel-plated steel plate in particular), and the like are used, from the perspective of obtaining corrosion-resistance and workability.
In either of the intended use, the steel plate is required to maintain a low contact resistance value. However, a Cr-containing steel plate, while having high corrosion-resistance, also has a Cr oxide layer on the surface of the steel plate. Thus, the surface resistance value of a Cr-containing steel plate has a large value. In order to use a Cr-containing steel plate for contact components and battery components, the surface resistance value is required to be lowered by performing some kind of surface treatment.
For example, for a positive electrode case of a lithium primary battery, a stainless steel plate (Cr-containing steel plate) such as SUS304, SUS430, SUS444, and the like are mainly used. To the inner face side of the positive electrode case, a carbon paste is applied in order to lower the contact resistance value of the stainless steel plate. However, the process of applying the carbon paste is cumbersome, and a large encumbrance is required for drying the carbon paste. For this reason, equipment costs, labor costs, energy consumption, and the like increase, and it is difficult to attempt reduction in production costs.
Due to technological innovation, power conservation, and the like of nowadays, further improvement in performance is being required for various components. Associated with the above, improvements in performances of materials for contact components, battery components, and the like are also being strictly asked. Most notably, suppressing the temporal change in contact resistance value so as to stabilize the resistance value for a long period of time, has become a significant task. Materials having a low contact resistance value in no way inferior to the conventional ones and having a small temporal change in resistance value, are in demand.
Patent Document 1 proposes coating a current collector for an alkaline battery with a noble metal, in order to improve the degree of electrical conductivity of the current collector. For the noble metal, gold, iridium, palladium, platinum, rhodium, ruthenium, and the like are used. As the method of coating, sputtering, painting method, dipping method, air atomization method, electrolysis, chemical vapor deposition, physical vapor deposition, ultrasonic air atomization, flame spraying, electric heat spraying, plasma spraying, and the like are proposed.
Patent Document 2 proposes using a surface-treated cold-rolled steel plate for a cylindrically-shaped battery case. Surface treatment is given by heat-treating a cold-rolled steel plate, and then performing hot-dipped plating. From the perspective of reducing wrinkles due to deep drawing, nickel, cobalt, iron, bismuth, indium, palladium, gold, zinc, and the like are used for the plating.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-39609
[Patent document 2] Japanese Laid-Open Patent Publication No. 2003-525346